Method for Coloring Ceramics Via Collidal Dispersion

ABSTRACT

In a method of coloring a ceramic material, a coloring solution consisting of metallic salts is introduced to a ceramic slurry. In a slip casting process, a coloring solution consisting of metallic salts is introduced to a ceramic slurry which is cast into green state bodies. A coloring solution that may comprise for example a metallic salt, a solvent, an organic solvent such as derivatives of propylene oxides, and an acid can be introduced to the slip casting process. Such a coloring solution can be added to the slip casting process. In a method, the coloring solution is thoroughly mixed with the ceramic slurry, after which a ceramic body is cast, dried and finally subjected to a sintering process. After final sinter, the resulting ceramic body possesses an innate color that is homogenous throughout its composition. The method is especially useful for coloring zirconia ceramic material used for making dental restorations.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of, and claims priority to, U.S.patent application Ser. No. 13/410,251, filed Mar. 1, 2012, which ishereby incorporated by reference in its entirety.

FIELD OF INVENTION

The present invention relates to the process in which a color solutionconsisting of metallic salts is introduced to a ceramic slurry andsubsequently slip cast into blocks of predefined dimensions.

BACKGROUND ART

Current techniques for coloring ceramics have limitations due toprocessing. At present, methods involve dipping a pre-sintered ceramicbody into a coloring solution containing metallic salts. Such methodsmay often result in inhomogeneous coloring on the surface of theceramic. In addition, the penetration of the coloring solution into thepores of the ceramic is largely affected by the components, composition,and properties of the solution. Depending on the constituents present inthe solution, little or no color penetration can result.

Such disadvantages arise when attempting to color a pre-sinteredceramic. This has prompted the need for an alternative method to color aceramic body. Such a method will remove the need to color a pre-sinteredceramic body and will result in a ceramic with innate color aestheticsthat are homogenous throughout the ceramic both internally and on thesurface. The present invention relates to creating a colored ceramicduring a slip casting process in which a color solution consisting ofmetallic salts is introduced into the slip and subsequently cast intoblocks.

Current methods for coloring ceramic bodies involve dipping apre-sintered ceramic of final shape into a coloring liquid. Theseprocesses require a wide range of soaking times and drying times toensure uniform and good quality results. After dipping, the ceramic bodyis dried and sintered, after which the final color is achieved.

The dipping methods currently used depend largely on the capillaryaction of the coloring liquid and the infiltration of said liquid intoceramic pores. The properties of the coloring liquid, such ascomposition, concentration, viscosity, pH, surface tension and wettingability directly influence the performance of the liquid. Should anyproperty not be optimized, undesirable results such as disproportionatecoloring or poor penetration of color into the ceramic body may result.

These methods color ceramic bodies after the ceramic has already beenprocessed and fabricated. The coloring agent is added to the ceramicsystem after initial fabrication of the ceramic. Therefore, the color isnot innate to the ceramic.

SUMMARY OF THE INVENTION

The present invention relates to a slip casting process by which aceramic slurry is cast into green state bodies. It is during this slipcasting that a coloring solution consisting of metallic salts isintroduced to the slurry and subsequently slip-cast.

A coloring solution may comprise for example a metallic salt, a solvent,an organic solvent such as derivatives of propylene oxides, and an acidcan be introduced to the slip casting process.

Such a coloring solution can be added to the slip casting process. Thesolution is thoroughly mixed with the ceramic slurry, after which theceramic body is cast, dried and finally subjected to a sinteringprocess.

After final sinter, the resulting ceramic body possesses an innate colorthat is homogenous throughout its composition.

The present invention utilizes metallic salts as the coloring agentpresent in the coloring liquid that is added to the slip castingprocess. The primary property of the metallic salt is such that issoluble in the solvent.

Metallic salts of transition metals from groups 3-12 on the periodictable can be used for the coloring solution. In addition, salts fromrare earth metals can be used as well. Metallic salts in the forms ofoxides or containing anions such as: Cl⁻, SO₄ ⁻, SO₃ ⁻, Br⁻, F⁻, NO₂ ⁻,and NO₃ ⁻ may be used.

The coloring solution, as it relates to the process by which a coloredceramic is made via slip casting, should contain metallic salts in therange of 0.01% to 5% by weight. The concentration of the metallic saltsis directly dependent on the target color that is to be achieved.

A preferred coloring solution also contains an organic solvent. Thepurpose for this solvent is to assure the homogeneity of the solutionthat contains the metallic salts. Derivatives of polypropylene oxide canbe used for this purpose.

The coloring solution, as it relates to the process by which a coloredceramic is made via slip casting, should be comprised of an organicsolvent of 1% to about 10% by weight.

A preferred coloring solution also contains acid. The purpose of thiscomponent is to maintain the colloidal stability of the coloringsolution when mixed into the ceramic slurry by upholding a stable pH. Anacidic pH level in the range of 1.0 to 4.0 is ideal.

The coloring solution, as it relates to the process by which a coloredceramic is made via slip casting, should be comprised of an acid of0.05% to about 5% by weight.

The primary property of the solvent is that it can dissolve the metallicsalts and facilitate a homogenous solution. Solvents can include water,alcohols, ketones, organic solvents, or mixtures thereof. The solventcomprises the majority of the solution by weight.

The present invention encompasses the process by which the coloredceramic is fabricated. Due to the unique properties of color thatincludes hue, chroma and value, varying ratios of coloring liquid areadded to the ceramic slurry before the slip casting process. The ratiois directly dependent on the target color that is to be achieved.

The colloidal slip, as it relates to the process by which a coloredceramic is made via slip casting, should have a ratio of grams ofcoloring liquid per gram of ceramic slurry in a range of about 0.01 toabout 1.00.

The present invention may be employed in the fabrication of a coloredceramic using a unique colloidal mixing process of a coloring agent intoa ceramic slurry. The coloring liquid is added to the ceramic slurry andafterward mixed to assure that a homogenous mixture is attained. Theslurry mixture is then slip cast into preformed molds.

Once slip cast, the ceramic bodies are dried before being subjected to asintering process. After final sinter, a homogeneously colored ceramicbody results.

An object of this invention is to create a ceramic body with a color ofspecific hue, chroma, and value. A further object is to create a processthat allows for a multitude of colors to be achieved.

Still a further object is to create a process that allows for thefabrication of a ceramic body with a homogeneous and uniform colorwithout adverse effects on the mechanical and optical properties of theceramic.

Still a further object is to create a coloring solution designed for theceramic fabrication process that results in a uniformly colored ceramic.

DETAILED DESCRIPTION

The present invention relates to color a ceramic body during the initialprocess and fabrication of the ceramic. A coloring solution is added tothe ceramic system during the processing stage. The result is a ceramicwith intrinsic color properties and complete color saturation.

A color solution of known compositions and concentrations can be used tocreate any color of desired hue, chroma and value. Using metallic saltsas the coloring agent, as well as a solvent to disperse the salts intosolution, this invention relates to a process that is designed forcoloring a ceramic during the manufacturing process of the material.

The process hereof ensures total and homogeneous color penetration intoa ceramic body. Such a ceramic body can then be cut or milled into anyshape or form. The final sintered ceramic body will be coloredcompletely without the need for an extra coloring process that normallytakes hours using conventional ceramic color methods.

The coloring solution and process hereof do not adversely affect themechanical and optical properties of the natural ceramic. Because thecoloring agent is mixed in a colloidal process, the coloring ions arehomogenously distributed through the ceramic's crystal structure.Therefore, the coloring ions are incorporated throughout the ceramic.

The present invention relates to the fabrication of a colored ceramicusing a unique colloidal mixing process of a coloring agent into aceramic slurry. Such a process can be applied to the dental industry,particularly in the fabrication of dental zirconia. At present, zirconiablocks are fabricated for the milling of dental crowns, bridges andcopings. Due to the natural strength and aesthetics of teeth, suchmechanical and optical properties are needed in dental ceramics.

At present, dental frameworks are milled from zirconia blocks. Becausethe natural color of zirconia is white, there is a need to color theceramic. The ceramic is therefore colored using conventional dippingmethods using coloring liquids. Current methods involve dipping apre-sintered zirconia framework of final shape into the color liquid fora specified soaking time period. Frameworks are subsequently dried andsintered. The dental industry at large uses the VITA classic shade guideas a standard for teeth aesthetics. These colors are unique in hue,chroma and value. Conventional color liquids are made to match theseproperties.

The present invention can eliminate the need for the coloring process ofthe pre-sintered dental frameworks. A zirconia dental ceramic can befabricated with the innate color properties of the final desiredproduct.

It is within the scope of the present invention to fabricate a dentalzirconia ceramic with a color that matches the hue, chroma and value ofthe VITA Classic dental shades.

It is also within the scope of the present invention to fabricate adental zirconia ceramic block that can be milled to a specified dentalframework of final shape and subsequently sintered. The resultingsintered zirconia framework will be of final shape and color thatmatches the VITA Classic shades.

Testing Results

Successful results have been achieved with the present invention. Acoloring solution of known concentration and composition and mixed itinto a colloidal zirconia slurry was used.

A coloring solution containing TbCl₃, CrCl₃, propylene glycol, 37%hydrochloric acid and de-ionized water was added to a zirconia slurry.

The exact composition of the coloring solution is as follows: 0.0914 wt% TbCl₃, 0.0609 wt % CrCl₃, 2.070 wt % propylene glycol, and 0.104 wt %hydrochloric acid. The balance was de-ionized water. The final pH of thesolution was measured to be 1.93.

A ratio of 0.0218 grams of coloring liquid per gram of zirconia slurrywas blended into a homogeneous mixture.

The slurry was subsequently slip cast into a disc shape and dried. Thiswas followed by a sintering process during which the discs were firedinto a pre-sintered bisque stage. After final sinter, the coloredceramic was cut to assure complete color saturation.

Total and homogenous coloring of the ceramic block was achieved. Using aVITA Easyshade instrument, the color was checked to verify if a dentalshade had indeed been matched. The final color matched closely to theVITA Classic shade B2.

A second test was performed to verify the results of the first. Acoloring liquid of different composition and concentration was used forprocessing.

The exact composition of the coloring solution is as follows: 0.122 wt %TbCl₃, 0.081 wt % CrCl₃, 2.030 wt % propylene glycol, and 0.104 w t%hydrochloric acid. The balance was de-ionized water. The final pH of thesolution was measured to be 1.96.

A ratio of 0.0218 grams of coloring liquid per gram of zirconia slurrywas blended into a homogeneous mixture.

The slurry was subsequently slip cast into a disc shape and dried. Thiswas followed by a sintering process during which the discs were firedinto a pre-sintered bisque stage. After final sinter, the coloredceramic was cut to assure complete color saturation.

Total and homogenous coloring of the ceramic block was achieved. Using aVITA Easyshade instrument, the color was checked to verify if dentalshade had indeed been matched. The final color matched closely to theVITA Classic shade A1.

Therefore, it will be understood that the present invention, as itrelates to a coloring liquid that is introduced to a colloidal processby which a colored ceramic is fabricated, has proven to be particularlyuseful in the dental industry to create a dental ceramic with intrinsiccolors that match the desired aesthetics of dental frameworks.

It will now be appreciated that the present invention relates to aunique process for providing selected coloring of ceramic materials inslip cast fabrication by introducing a coloring solution of metallicsalts into the slurry. This invention is particularly applicable to thecoloring of slip cast fabricated zirconia blocks for use as dentalrestorations such as full contour crowns, bridges and the like. Whileexemplary embodiments have been disclosed herein, the scope hereof willbe limited only by the appended claims and their legal equivalents.

The invention claimed is:
 1. A method of making a colored zirconiaceramic body comprising; a) forming a coloring solution consistingessentially of 0.01% to 5% by weight of at least one metallic salt byweight of the coloring solution, a solvent, and optionally, an acid,wherein the at least one metallic salt is soluble in the solvent; b)choosing an amount of the coloring solution and an amount of a zirconiaceramic slurry in a ratio of about 0.01 gram to about 1.00 gram coloringsolution per gram of zirconia ceramic slurry to provide a selected hue,chroma, and value to a colored zirconia ceramic body; c) adding theamount of the coloring solution to the amount of a zirconia ceramicslurry; d) mixing to distribute the coloring solution throughout thezirconia ceramic slurry to form a colored zirconia slurry; and e)slip-casting the colored zirconia slurry to form a colored zirconiaceramic body made predominantly of zirconia.
 2. The method of claim 1,wherein the at least one metallic salt is of transition metals fromgroup 3-12 of the periodic table.
 3. The method of claim 1, wherein theat least one metallic salt is of rare earth metals.
 4. The method ofclaim 1, wherein the at least one metallic salt is in the form of oxidesor contains anions.
 5. The method of claim 1, wherein the at least onemetallic salt contains anions selected from Cl⁻, SO₄ ⁻, SO₃ ⁻, Br⁻, F⁻,NO₂ ⁻, and NO₃ ⁻.
 6. The method of claim 1, wherein the at least onemetallic salt is TbCl₃ and CrCl₃.
 7. The method of claim 1, wherein thesolvent is selected from water, an organic solvent, or mixtures thereof.8. The method of claim 1, further comprising firing the colored zirconiaceramic body to a bisque stage.
 9. The method of claim 1, wherein stepb) comprises choosing an amount of the coloring solution and an amountof a zirconia ceramic slurry in a ratio to provide a selected hue,chroma, and value of a dental shade in a final sintered product madefrom the colored zirconia ceramic body.
 10. The method of claim 1,wherein a final sintered ceramic body made by sintering the coloredzirconia ceramic body comprises color penetration throughout the finalsintered ceramic body.
 11. A method of coloring a zirconia ceramiccomprising; a) forming a coloring solution consisting essentially of atleast one metallic salt selected from transition metals from groups 3-12of the periodic table and rare earth metals, and a solvent, andoptionally, an acid, wherein the at least one metallic salt is solublein the solvent; b) choosing an amount of the coloring solution and anamount of a zirconia ceramic slurry in a ratio of about 0.01 gram toabout 1.00 gram coloring solution per gram of the zirconia ceramicslurry to provide a selected hue, chroma, and value to a coloredzirconia ceramic body; c) adding the amount of coloring solution to theamount of a zirconia ceramic slurry; and d) mixing to distribute thecoloring solution throughout the zirconia ceramic slurry to form acolored zirconia slurry that may be slip cast to form a colored zirconiaceramic body.
 12. The method recited in claim 11, wherein in step a) thecoloring solution contains an acid.
 13. The method recited in claim 12,wherein in step a) the acid comprises between 0.05% to 5% by weight ofthe coloring solution.
 14. The method recited in claim 11, wherein instep a) the solvent is selected from water, alcohols, ketones, organicsolvents, and mixtures thereof.
 15. The method recited in claim 11,wherein the solvent comprises a derivative of a propylene oxide.
 16. Themethod of claim 11, wherein metallic salts comprise 0.01% to 5% byweight of the coloring solution.
 17. The method of claim 11, whereinmetallic salts comprise 0.01% to 5% by weight of the coloring solutionand the coloring solution comprises TbCl₃ and CrCl₃.
 18. The method ofclaim 11, further comprising slip casting the colored zirconia ceramicslurry into a colored zirconia ceramic body that is predominantlyzirconia.
 19. The method of claim 18, further comprising firing thecolored zirconia ceramic body to a bisque stage.
 20. The method of claim18, wherein step b) comprises choosing an amount of the coloringsolution and an amount of a zirconia ceramic slurry in a ratio toprovide a selected hue, chroma, and value of a dental shade in a finalsintered product made from the colored zirconia ceramic body.